Exercise Addicts Can Blame Their Brains

Aug. 28, 2009

By LAUREN COXABC News Medical Unit

Stan Jensen has completed 20 marathons and 125 ultra marathons in his lifetime.

Courtesy Stan Jensen

Some people are so athletic -- running daily in rain, wind and heat in sickness and in health -- that most people wonder if they are masochists. But new research shows that they may just be addicted to exercise.

Stan Jensen, author of Run100s.com, has competed in 20 marathons and 125 ultramarathons in his lifetime. He said he considered each race "fun," but agrees there are sometimes other motivations at work among ultra runners.

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"Take the Boston marathon: for a lot of runners that's their goal. They say 'wow that was hard, I'm glad I did it' and they go back to mowing the lawn," he said.

But Jensen wasn't satisfied. After many city marathons he moved to marathons on trails, and then he morphed to an ultra marathon, which is any race longer than the standard 26 miles in a marathon. Eventually, Jensen was doing 100-mile races.

Jensen's not alone in his enthusiasm. This week Robert Donahue of Minneapolis wanted to help recruit male mentors for his local Big Brothers Big Sisters. To do it, he decided he would run 100 miles in five days, which amounts to a little less than a marathon each day.

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Other enthusiasts have set up races in horrible conditions such as the Badwater Ultramarathon in Death Valley (135 miles in temperatures up to 130 degrees), or the annual Antarctic Ice Marathon(82 miles in wind chills of -20).

Jensen insists that the soft trails and slower pace of an ultramarathon are easier on the body than the fast-paced pounding on pavement involved in most marathons. But ultramarathons lure runners who seek a challenge to keep up the "runner's high."

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"There was a time at which I was definitely addicted to running. I enjoyed it, I enjoyed the way I felt when I ran and I enjoyed the feeling of accomplishment when I finished," said Jensen. "Running is also a form of escape. If you have chores, you have a choice: maybe I can just go run for a couple of hours and mow the lawn later."

But he will admit there's a bit of extreme thinking behind some among ultra marathoners.

"I also know people in my sport who are former alcoholics, or heroin addicts. They say 'you know, I have a problem with addiction, but this is the healthiest I addiction I can have'," said Jensen.

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A new study in the August edition of the journal Behavioral Neuroscience showed running may indeed be addictive to the brain in the same way as heroin or morphine.

Runner's High Equivalent to Low Doses of Heroin?

Scientists have long known that exercising can release endorphins in the brain, and that some runners need to keep adding distances to feel that "high." However, it is not known if running forms a true addiction.

To test this, scientists turned to rats. It turns out rodents also keep increasing their amount of time on the running wheel like humans do.

Researchers at Tufts University let one group of rats become increasingly avid runners, and forced another group of rats to stay lazy in a cage with no hamster wheel.

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When the researchers injected both groups of mice with a drug called Naloxone that is used for heroin withdrawal, the rats who had become exercise fanatics showed withdrawal symptoms similar to human heroin addicts on Naloxone -- their teeth shattered, and their bodies shook in tremors.